from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
# 扩展包
db=SQLAlchemy()
migrate=Migrate()
# 扩展包的连接init
def exist_init(app):
    db.init_app(app=app)
    migrate.init_app(app=app,db=db)
    with app.app_context():
        db.create_all()